Methods and apparatuses for freeform additive manufacturing of engineering polymers

ABSTRACT

A polymer three-dimensional (3D) printing methodology is disclosed for freeform fabrication of polymeric structures under ambient conditions without the use of printed support structures. The build material can be dissolved in a suitable solvent for 3D printing. The polymer solution can be printed in (e.g., continuously printed using a moving dispensing nozzle) a yield-stress support bath to form an intermediate article. The intermediate article may be liquid or only partially coagulated after being printed into the yield-stress support bath. The yield-stress support bath may be at least partially disposed within a container, and the container may be immersed in a post-treatment coagulation solution to remove some or all of the solvent, causing the build material to fully solidify to form a finished article from the intermediate article.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. Non-Provisional patentapplication Ser. No. 17/200,284, filed Mar. 12, 2021 and entitled“Methods and Apparatuses for Freeform Additive Manufacturing ofEngineering Polymers,” which is a continuation of U.S. Non-Provisionalpatent application Ser. No. 16/703,686, filed Dec. 4, 2019 and entitled“Methods and Apparatuses for Freeform Additive Manufacturing ofEngineering Polymers,” which issued as U.S. Pat. No. 10,974,441 on Apr.13, 2021, which claims priority to, and the benefit of, U.S. ProvisionalPatent Application Ser. No. 62/778,479, filed Dec. 12, 2018 and entitled“Solvent Enabled Freeform Additive Manufacturing of Engineering Polymersat Room Temperature,” the entire contents of each of which are herebyincorporated herein by reference in their entireties for all purposes.

TECHNICAL FIELD

Embodiments described herein relate generally to additive manufacturing,and more particularly to freeform additive manufacturing of polymericmaterials.

BACKGROUND

Additive manufacturing, also referred to as three-dimensional (3D)printing, encompasses a range of technologies used to fabricate parts byadding material to build up the part rather than by subtracting unwantedmaterial away from a bulk starting workpiece. Generally, 3D printingforms parts by depositing and/or solidifying build materiallayer-by-layer in computer-controlled patterns generated from a digitalpart model; each layer forms a thin slice of the complete part and thelayers are integrated to form a tangible part based on the digitalmodel. In fused deposition modeling (FDM), a widely implemented type of3D printing, a thermoplastic build material in the form of a filament ismelted and extruded from a hot tip to generate 3D parts layer-by-layerin a controlled spatial pattern; as in other 3D printing processes, thepart is first generated as a computer model, then transformed intocommands for a 3D printer. FDM can be used for fabricating prototypesand products from rigid thermoplastic polymer materials, such aspoly(lactic acid) (PLA) and acrylonitrile-butadiene-styrene (ABS).

As FDM printing technology continues to mature, there is a demand formore versatile approaches which are compatible with a wider range ofpolymeric build materials to fabricate more complex prototypes andend-use parts with a broad range of properties and features.

SUMMARY

A polymer three-dimensional (3D) printing method and associatedapparatus are disclosed for fabrication of 3D printed structures andarticles. In some embodiments, the fabrication may be freeformfabrication. In some embodiments, the 3D printed structures and articlesmay be formed from a build material, such as a polymeric material in apolymer/solvent solution. In some embodiments, 3D printed structures andarticles may be fabricated under ambient conditions and/or without theuse of printed support structures which would need to be removed after3D printing in order to achieve the finished structure or article. Insome embodiments, a build material can be dissolved in a suitablesolvent or solvent solution (e.g., solvent/non-solvent mixture) for 3Dprinting. In some embodiments, the build material can comprise one ormore polymers or a polymer solution. In some embodiments, the buildmaterial can be disposed within a support bath, such as a yield-stresssupport bath. In some embodiments, the yield-stress support bath cancomprise one or more yield-stress support materials having a particularcomposition and particular mechanical properties such that theyield-stress support bath is suitable to support the build material oncedisposed within the yield-stress support bath. In some embodiments, toform an intermediate article in the yield-stress support bath comprisinga yield-stress support material, the build material may be printed intoand supported by the yield-stress support material. The intermediatearticle may be a liquid or only partially coagulated or solidified afterbeing printed into the yield-stress support material. In someembodiments, the yield-stress support bath may be at least partiallycontained within a container. In some embodiments, once the buildmaterial is disposed within the yield-stress support bath, the containerat least partially containing the yield-stress support bath may then beimmersed in a post-treatment coagulation solution to further or fullysolidify the printed build material. In some embodiments, heat, achemical reactant, electromagnetic radiation, and/or the like may bedisposed within or transmitted into the container to further or fullysolidify the printed build material. In some embodiments, by solidifyingthe printed build material within the yield-stress support bath, afinished article may be formed from the intermediate article.

In some embodiments, a method for three-dimensional printing of afinished article can include, optionally, dissolving a polymericmaterial in a solvent to form a build material. In some embodiments, thebuild material can comprise any suitable polymeric material such as athermoplastic. In some embodiments, a polymeric material can bedissolved or dispersed in any suitable solvent. In some embodiments,such a solvent can comprise dimethyl sulfoxide (DMSO), and/or the like.In some embodiments, to form the build material, the polymeric materialcan be dissolved in the solvent partially or fully, at about roomtemperature (about 20° C. to about 25° C.), or at an elevatedtemperature, while being stirred, shaken, agitated, bombarded withelectromagnetic radiation and/or ultrasonic sound waves, or the like. Insome embodiments, one or more solvents can be chosen that are capable ofbreaking down the build material without causing molecular degradationor a reduction in the degree of polymerization (DP). Conventionaladditive manufacturing and 3D printing techniques for polymericmaterials typically requires melting the polymeric material at leastpartially if not fully to facilitate the communication and build-up ofthe article using the polymeric material. These conventional additivemanufacturing and 3D printing techniques for polymeric materials canrequire high heat, which can make the process costly, dangerous,time-consuming, and limiting in terms of the reusability of printingmaterials. By contrast, the room temperature process according to someembodiments described herein requires no heating of the printingmaterials, no thermal deterioration of the polymers, and can eliminatethe process step from conventional additive manufacturing and 3Dprinting methods of heating and/or melting the polymeric material.

In some embodiments, the method can further include dispensing,extruding, injecting, or otherwise disposing the build material, e.g., adissolved polymeric material, into the yield-stress support bath to forman intermediate article. In some embodiments, the intermediate articleonly partially solidified. Additionally or alternatively, in someembodiments, the build material, e.g., a dissolved polymeric material,can be injected, spun, inserted, communicated, dropped, conveyed, orotherwise dispensed or disposed within the yield-stress support bathsuch that the yield-stress support bath can facilitate at least partialformation of the article. Regardless of the particular manner in whichthe build material, e.g., the dissolved polymeric material, is disposed,dispersed, injected, extruded, spun, sputtered, dropped, or dispensedinto the yield-stress support bath, or otherwise comes to be within theyield-stress support bath, the yield-stress support bath can providesufficient support for the at least partial formation of theintermediate article. Said otherwise, in some embodiments, the buildmaterial can be disposed in particular quantities at particularlocations within the yield-stress support bath and/or at a particularrate while a disposing nozzle is moved along a particular path throughthe yield-stress support bath. In some embodiments, the particularvolume of the yield-stress support bath in which the build material isdisposed can relate to the eventual volume of the intermediate article.

According to some embodiments, the yield-stress support material in theyield-stress support bath can provide sufficient support for at leastpartial solidification or coagulation of the build material solution,facilitating the formation of the intermediate article directly withinand supported by the yield-stress support material such that theintermediate article is formed free of printed support structures. Suchsupport structures are often used in conventional additive manufacturingand 3D printing techniques and usually must be trimmed away afterformation of the intermediate or finished article. By forming theintermediate article without printed supports in the yield-stresssupport bath, the methods described herein can reduce or eliminate thelabor-intensive, costly, and time-consuming manufacturing stage oftrimming away the printed support structures once the finished articleis formed or otherwise printed.

In some embodiments, the build material can comprise a polymericmaterial, such as at least one from among thermoplastic polymer,thermosetting polymers, acrylonitrile-butadiene-styrene, polyurethane,acrylic, poly(acrylonitrile), polyolefins, polyvinyl chlorides, nylons,fluorocarbons, polystyrenes, polyethylene, ultra-high molecular weightpolyethylene, polypropylene, polybutene, polymethylpentene,polyisoprene, copolymers thereof, and their combinations, mixturescontaining two or more of the following polyethylene, ultra-highmolecular weight polyethylene, and polypropylene, as well as, mixturesof the foregoing with copolymers such as ethylene-butene copolymers andethylene-hexene copolymers, thermosetting plastics, such as polyimide(PI), poly amide (PA), and poly amide imide (PAI), polypropylene (PP),polyethylene (PE), ethylene vinylacetate (EVA), poly(ethyleneterephthalate) (PET), poly(vinyl acetate) (PVA), polyamide (PA), acrylicadhesives, ultraviolet (UV)/electron beam (EB)/infrared (IR) curableresin, polyether ether ketone (PEEK), polyethylene naphthalate (PEN),polyethersulfone (PES), polyphenylene sulfide (PPS), polyphenylene oxide(PPO), combinations thereof, and/or the like.

In some embodiments, the solvent can comprise at least one from amongdimethyl sulfoxide (DMSO), dimethylformamide (DMF), acetonitrile,ethanol, combinations thereof, and/or the like.

In some embodiments, the yield-stress support bath can comprise apolymer/solvent mixture, such as a Carbopor®-based solvent-rich supportbath. In some embodiments, the yield-stress support bath can compriseany suitable rheological additive as described herein dissolved ordispersed in a suitable solvent, such as but not limited to DMSO, DMF,acetonitrile, ethanol and the like. By way of example only, ayield-stress support material can include Carbopol® (a type ofrheological additive), DMSO, and water. More specifically, a supportbath according to at least one embodiment can include 1.5% Carbopol® byweight or by volume, mixed into an approximately 9:1 v/v ratio ofDMSO:H₂O. In some embodiments, other rheological additives such as asynthetic layered silicate, e.g., Laponite XLG, and the like can beadded to prepare the solvent-based support bath material. Rheologicaladditives can include shear thinning additives, shear thickeningadditives, thixotropic rheology modifiers, and other such additives. Insome embodiments, the additive can be chosen carefully such that theyield-stress support bath provides sufficient yield-stress support tothe printed polymer/solvent solution upon injection and so that theviscosity and chemical properties of the yield-stress support bathdisallows or partially disallows mixing and diffusion or solvation ofthe printing/build material solution or components thereof. In someembodiments, the yield-stress support material can be prepared or causedto be prepared by mixing together a suitable rheological additive and asolvent, mixture of solvents, and/or solvent/non-solvent mixture, andthe solution can be allowed to “set” for a sufficient period of time,e.g., 12 hours. In some embodiments, the period during which thesolution sets may be helpful and/or necessary for the resultingyield-stress support material in the yield-stress support bath to havesuitable rheological and mechanical properties to support freeformprinting of the intermediate article in the yield-stress support bath.In other embodiments, the yield-stress support material may not requireany or substantially any, or may require only a very short period oftime to set, before the yield-stress support material exhibits suitablerheological and/or mechanical properties such that the yield-stresssupport material supports freeform printing of the intermediate articlein the yield-stress support bath. Many other compositions andconcentrations of support bath material and additives thereto weretested, are contemplated, and are within the scope of the currentdisclosure. Some, but not all, of the suitable compositions,concentrations, methods, apparatuses, parameters, rheological ormechanical properties, and printing materials are described hereinbelow.

The method can further include immersing the intermediate article in apost-treatment coagulation solution to fully solidify the intermediatepart into the finished article. The post-treatment coagulation solutioncan comprise any suitable material, for instance one or more of water,deionized water, ethanol, or the like.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, thecombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning consistent withthe particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIG. 1 illustrates a process flow diagram of a method of 3D printing,according to an embodiment.

FIG. 2A provides a photographic image of an article formed fromacrylonitrile butadiene styrene, according to some embodiments.

FIG. 2B provides a photographic image of an article formed fromacrylonitrile butadiene styrene by freeform additive manufacturing usinga yield-stress support bath, according to some embodiments.

FIG. 2C provides a photographic image of an article formed fromacrylonitrile butadiene styrene by freeform additive manufacturing usinga yield-stress support bath, according to some embodiments.

FIG. 2D provides a photographic image of an article formed fromacrylonitrile butadiene styrene by freeform additive manufacturing usinga yield-stress support bath, according to some embodiments.

FIG. 2E provides a photographic image of an article formed fromacrylonitrile butadiene styrene by freeform additive manufacturing usinga yield-stress support bath, according to some embodiments.

FIG. 2F provides a photographic image of an article formed from anacrylic by freeform additive manufacturing using a yield-stress supportbath, according to some embodiments.

FIG. 2G provides a photographic image of an article formed from anacrylic by freeform additive manufacturing using a yield-stress supportbath, according to some embodiments.

FIG. 2H provides a photographic image of an article formed frompolyurethane by freeform additive manufacturing using a yield-stresssupport bath, according to some embodiments.

FIG. 2I provides a photographic image of an article formed frompolyurethane by freeform additive manufacturing using a yield-stresssupport bath, according to some embodiments.

FIG. 2J provides a photographic image of an article formed frompolyacrylonitrile by freeform additive manufacturing using ayield-stress support bath, according to some embodiments.

FIG. 2K provides a photographic image of an article formed frompolyacrylonitrile by freeform additive manufacturing using ayield-stress support bath, according to some embodiments.

FIG. 2L provides an graphic representation of a gear vase design for anadditive manufacturing process, according to some embodiments.

FIG. 2M provides an graphic representation of a spiral cone design foran additive manufacturing process, according to some embodiments.

FIG. 2N provides an graphic representation of a T-junction design for anadditive manufacturing process, according to some embodiments.

FIG. 3 illustrates a process flow diagram of a method for 3D printingarticles into a yield-stress support bath, according to an embodiment.

FIG. 4 provides a photographic image of an ABS part printed in ayield-stress support bath, according to an embodiment.

FIG. 5 is a graphical representation of the tensile modulus of anarticle, printed according to a freeform additive manufacturing methoddescribed herein, compared to an article printed using conventional FDM.

FIG. 6A provides a photographic image of an article formed from a 10%polyurethane build material by freeform additive manufacturing using ayield-stress support bath, according to some embodiments.

FIG. 6B provides a photographic image of an article formed from a 30%polyurethane build material by freeform additive manufacturing using ayield-stress support bath, according to some embodiments.

FIG. 6C provides a photographic image of an article formed from a 20%acrylonitrile butadiene styrene build material by freeform additivemanufacturing using a yield-stress support bath, according to someembodiments.

FIG. 6D provides a photographic image of an article formed from a 35%acrylonitrile butadiene styrene build material by freeform additivemanufacturing using a yield-stress support bath, according to someembodiments.

FIG. 7A provides a photographic image of an article formed from a 30%acrylonitrile butadiene styrene build material by freeform additivemanufacturing using a yield-stress support bath comprising 1.5% Carbopol940 in 85% dimethyl sulfoxide, according to some embodiments.

FIG. 7B provides a photographic image of an article formed from a 30%polyurethane build material by freeform additive manufacturing using ayield-stress support bath comprising 1.5% Carbopol 940 in 85% dimethylsulfoxide, according to some embodiments.

FIG. 7C provides a photographic image of an article formed from a 30%acrylonitrile butadiene styrene build material by freeform additivemanufacturing using a yield-stress support bath comprising 1.5% Carbopol940 in 95% dimethyl sulfoxide, according to some embodiments.

FIG. 7D provides a photographic image of an article formed from a 30%polyurethane build material by freeform additive manufacturing using ayield-stress support bath comprising 1.5% Carbopol 940 in 95% dimethylsulfoxide, according to some embodiments.

FIG. 8 illustrates processes for printing in a support bath withcoagulation and printing in a support bath without coagulation,according to an embodiment.

DETAILED DESCRIPTION

Additive manufacturing, also referred to as three-dimensional (3D)printing, encompasses a range of technologies used to fabricate parts bybuilding material up rather than by subtracting unwanted material awayfrom a bulk starting workpiece. Conventionally, printed parts are formedusing 3D printing by depositing and/or solidifying a build materiallayer-by-layer in computer-controlled patterns generated from a digitalpart model; each layer forms a thin slice of the complete part and thelayers are integrated to form a tangible part based at least in part onthe digital model. Another conventional 3D printing technique is fuseddeposition modeling (FDM), a widely implemented type of 3D printing, inwhich a thermoplastic build material in the form of a filament is meltedand extruded from a hot tip to generate 3D parts layer-by-layer in acontrolled spatial pattern; as in other 3D printing processes, the partis first generated as a computer model, then transformed into commandsfor a printer. FDM can be used for fabricating prototypes and productsfrom rigid thermoplastic polymer materials, such as poly(lactic acid)(PLA) and acrylonitrile-butadiene-styrene (ABS).

Additive manufacturing is a powerful tool for production and prototypingusing a wide range of materials. Conventional 3D printing methods, forinstance conventional FDM methods, may be suitable for a limited rangeof polymeric materials and geometries, however there are many articles,materials, and production scenarios for which using such conventional 3Dprinting approaches compromises article printing precision, articlemechanical properties, and/or the cost/time associated with production.

Typically, conventional 3D printing methods such as FDM methods involvemelting the 3D printing/build material to enable iterative, layereddeposition, which may result in thermal damage to the polymer (moleculardegradation) as well as undesirable thermal residual stress. Forinstance, certain polymeric materials such as non-thermoplastic polymersmay degrade upon heating instead of melting. Thus, these materialscannot or should not be melt processed. Other materials are difficult tohandle in the filament form necessary for conventional FDM since theyare prone to damage from the feed mechanism, stretching, distortion, andirregular flow; all of which can result in inconsistent printingperformance and unpredictable part properties. Sometimes it can bedifficult to FDM print high-temperature engineering polymers. Forinstance, even if high temperature plasticity is achievable for mostpolymers, the thermal residual stress within FDM parts may also be aconcern. Such thermal residual stress within FDM parts may be a resultof thermal gradients between individual deposited layers and between theprinted part and its surroundings. Oftentimes, such thermal residualstress can lead to deformation of a FDM part, can lead to deficientmechanical properties, can reduce the mechanical, optical, thermal,radiative, and/or chemical stability of the FDM part, and/or can lead toaesthetic and/or operability issues. Such deficiencies and issues maypresent themselves at some time after FDM printing of the FDM part, ormay present themselves, alone or in combination with other issues,sometime after FDM printing, such as after some amount of use of thepart or after some exposure of the FDM part to an environmental or aman-made stimulus.

Additionally, undesirable surface and interface characteristics at theinterface between two neighboring filaments or layers may reduce themechanical strength and other mechanical properties of the finishedarticle. As such, FDM often results in a finished part that has reducedinternal mechanical strength, which can lead to a reduction in theoverall mechanical properties of the FDM printed part or portionsthereof.

Furthermore, current FDM technology generally requires the use of atemporary support material which is printed alongside the part to ensurethat overhanging regions and other details remain intact, especially forsoft polymer build materials but also often for other build materials.This requirement for support structures to be concurrently printed withthe finished article increases the complexity of the printing machinerysince it must handle multiple materials, the complexity of the code toappropriately deposit the support material, the fabrication time sinceswitching heads and printing support structures are both time consuming,and the post-processing time since the support material must be removedafter printing is complete. Thus, a more robust methodology for 3Dprinting engineering polymers including soft and/or non-thermoplasticmaterials is of great interest. It is desired that this process beimplementable in ambient conditions to avoid thermal residual stress onthe printed article, minimize interfaces between filaments or layers,and reduce the use of printed support structures to maximize fabricationefficiency.

Thus, the inventors have conceived of and diligently reduced to practicemultiple embodiments of a method and an associated apparatus forthree-dimensional (3D) printing that enables freeform fabrication ofprinted structures and articles. According to some embodiments, suchfreeform fabrication can be carried out under ambient conditions.According to these and/or other embodiments, such freeform fabricationcan be carried out without the use of support structures (e.g., printedsupport structures, solid support structures, support structures thatare inherent to the printed article or the printing platform, supportstructures that should or must be removed after printing and before theprinted article is ready for use, and/or the like). According to someembodiments, a build material (e.g., a polymeric material) can bedissolved in a solvent, a solvent mixture, or a mixture of solvent(s)with non-solvents (e.g., a rheological modifier and/or the like) forextrusion printing. The build material/solvent solution (which is alsoreferred to interchangeably herein as the “ink,” the “printing mixture,”the “printing medium,” the “polymer mixture,” and the “polymersolution,”) can be printed in and supported by a yield-stress supportbath to form an entire 3D part in the yield-stress support material. Theprinted part may be still liquid or only partially coagulated. Afterprinting, the yield-stress support bath container can be immersed in apost-treatment coagulation solution to solidify the printed polymermaterial, and the solid printed part can then be removed from theyield-stress support material and post-treatment bath.

Referring now to FIG. 1 , a method 10 for three-dimensional printing ofa finished article can include dispensing a mixture of a polymericmaterial and a solvent into a yield-stress support bath, at 11, andallowing the intermediate article to only partially coagulate orsolidify, forming an intermediate article, at 12. In some embodiments,the dissolved polymeric material can be injected, spun, inserted,communicated, dropped, conveyed, or otherwise dispensed within theyield-stress support bath such that the yield-stress support bath canfacilitate at least partial formation of the article. Regardless of theparticular manner in which the dissolved polymeric material is dispensedwithin the yield-stress support bath, the yield-stress support bath canprovide sufficient support for the at least partial formation of theintermediate article. According to some embodiments, the yield-stresssupport bath can provide sufficient support for the at least partialformation of the intermediate article such that the intermediate articleis formed free of printed support structures. Such support structuresare used extensively across the array of conventional additivemanufacturing and 3D printing techniques and are often required to betrimmed away after formation of the intermediate or finished article. Byforming the intermediate article without printed supports in theyield-stress support bath, the methods described herein can eliminatethe labor-intensive, costly, and time-consuming process step of trimmingaway the printed support structures once the article is fully formed.

In some embodiments, the polymeric material can include at least onefrom among thermoplastic polymer, thermosetting polymers,acrylonitrile-butadiene-styrene, polyurethane, acrylic,poly(acrylonitrile), polyolefins, polyvinyl chlorides, nylons,fluorocarbons, polystyrenes, polyethylene, ultra-high molecular weightpolyethylene, polypropylene, polybutene, polymethylpentene,polyisoprene, copolymers thereof, and their combinations, mixturescontaining two or more of the following polyethylene, ultra-highmolecular weight polyethylene, and polypropylene, as well as, mixturesof the foregoing with copolymers such as ethylene-butene copolymers andethylene-hexene copolymers, thermosetting plastics, such as polyimide(PI), poly amide (PA), and poly amide imide (PAI), polypropylene (PP),polyethylene (PE), ethylene vinylacetate (EVA), poly(ethyleneterephthalate) (PET), poly-vinyl acetate (PVA), polyamide (PA), acrylicadhesives, ultraviolet (UV)/electron beam (EB)/infrared (IR) curableresin, polyether ether ketone (PEEK), polyethylene naphthalate (PEN),polyethersulfone (PES), polyphenylene sulfide (PPS), polyphenylene oxide(PPO), and any combinations thereof.

In some embodiments, the solvent can include at least one from amongdimethyl sulfoxide (DMSO), dimethylformamide (DMF), acetonitrile,ethanol, combinations thereof, and the like.

The method 10 can further include exposing the intermediate article to apost-treatment coagulation solution to fully solidify the intermediatearticle, forming the finished article, at 13. The post-treatmentcoagulation solution can comprise any suitable material with regard tothe 3D printing material (e.g., the build material), the solvent chosen,and/or the yield-stress support material, for instance one or more ofwater, deionized water, ethanol, and the like. Many other compositionsand concentrations of post-treatment coagulation solution were tested,are contemplated, and are within the scope of the current disclosure.

The method 10 can optionally include dissolving the polymeric materialin the solvent to form the mixture of the polymeric material and thesolvent, at 14. The polymeric material can be dissolved or dispersed inany suitable solvent, such as but not limited to dimethyl sulfoxide(DMSO), and the like. The polymeric material can be dissolved ordispersed in the solvent partially or fully, at about room temperature(about 20° C. to about 25° C.). Alternatively, the polymeric materialcan be dissolved or dispersed at a temperature less than or greater thanabout room temperature. In some embodiments, dissolution of the polymermaterial for 3D printing can be accomplished with the help of otherprocesses or energies, such as by stirring, shaking or agitating thepolymeric material/solvent mixture, by bombarding the mixture withultrasonic waves, electromagnetic energy, or other energies, and/or thelike. The solvent or solvents can be chosen such that the solvent canbreak down the build material without causing molecular degradation or areduction in the degree of polymerization (DP). Conventional additivemanufacturing and 3D printing techniques for polymeric materialstypically requires melting the polymeric material at least partially ifnot fully to facilitate the communication and build-up of the articleusing the polymeric material. These conventional additive manufacturingand 3D printing techniques for polymeric materials can require high heatto melt the build material, which can make the conventional processescostly, relatively more dangerous, time-consuming, and/or limiting interms of the reusability of printing materials. By contrast, the method10 described herein, according to some embodiments, is carried out at oraround room temperature and therefore does not require heat to beapplied during the process, does not induce thermal deterioration of thepolymers, and eliminates the process step of heating and/or melting thepolymeric material.

The method 10 can optionally include mixing a rheological additivematerial with a second solvent, mixture of solvents, and/orsolvent/non-solvent mixture and allowing the rheological additivematerial mixture to become at least partially solid-like, forming theyield-stress support bath, at 15. In some embodiments, the yield-stresssupport bath can be a rheological additive-solvent mixture, such as aCarbopol®-based solvent-rich support bath. In some embodiments, theyield-stress support bath can comprise any suitable rheological additiveas described herein dissolved or dispersed in a suitable solvent, suchas but not limited to DMSO, DMF, acetonitrile, ethanol and the like, orany combination thereof. By way of example only, a support bath materialcan include at least Carbopol®, DMSO, and water. More specifically, asupport bath according to at least one embodiment can include 1.5%Carbopol® by weight or by volume, mixed into an approximately 9:1 v/vratio of DMSO:H₂O. In some embodiments, additives such as a syntheticlayered silicate, e.g., Laponite XLG, and the like can be added to theyield-stress support material. Rheological additives can include shearthinning additives, shear thickening additives, thixotropic rheologymodifiers, and other such additives. In some embodiments, the additivecan be chosen carefully such that the yield-stress support bath providessufficient yield-stress support to the printed polymer/solvent solutionupon injection and so that the viscosity and chemical properties of theyield-stress support bath disallows mixing and extensive diffusion orsolvation of the printing/build material solution or components thereof.In some embodiments, the yield-stress support material can be preparedor caused to be prepared by mixing together the suitable rheologicaladditive and a solvent, mixture of solvents, or solvent/non-solventmixture and the solution can be allowed to “set” for a period of time,e.g., 12 hours, before printing is carried out. Many other compositionsand concentrations of support bath material and additives thereto weretested, are contemplated, and are within the scope of the currentdisclosure.

This method 10 can be carried out for the fabrication of arbitrary partsin arbitrary orientations. In other words, the complexity, costliness,and time necessary to carry out fabrication is at least partiallydecoupled from the shape, dimensions, and complexity of the articlebeing fabricated. The implications for practical applications aresurprising and significant. Conversely, 3D printing a polymeric article,e.g., an article having high complexity, according to conventionalprocesses requires a not insignificant amount of thought, time, and/orcomputing power be dedicated to the printing orientation of the part tomaximize printing precision and minimize printing time, requires carefulplacement of printed support structures such that the printed article issufficiently stabilized and such that the printed support structures areminimized, and requires time, labor, and therefore cost to trim away thesupport structures from the finished article, a process which sometimesdamages the printed article such that the printed article must bescrapped. The 3D printing methods, e.g., the method 10, described hereincan eliminate the need for a particular orientation, are not renderedmore time-consuming or costly with increasing article complexity, and donot require support structures to be printed concurrent to the printingof the article, meaning less 3D printing/build material is wasted andthe printed support structure trimming step is eliminated completely.The advantages in terms of production cost and time for 3D printedarticles, among other advantages associated with these methods, areclear. Select finished articles formed from various materials accordingto various embodiments of the method, e.g., the method 10, areillustrated in FIGS. 2A-2G according to article designed illustrated inFIGS. 2L-2N.

For example, ABS parts were printed according to the method 10 forcomparison with traditional FDM results, while soft poly(urethane) andrigid poly(acrylonitrile) and acrylic build materials were printedaccording to the method 10 to illustrate the versatility of the processand highlight the effects of fabrication parameters on the printedparts.

Solid blocks, branching tubular shells, intricate solid parts, andhollow parts with complex surface textures, among other structures andform factors, were printed to demonstrate the print fidelity, achievableinfill density and morphology, resolution, and printing precision of theproposed methodology. Solid blocks illustrate the surface quality, shapefidelity, and ability to form bulk parts, while tubular structuresdemonstrate the excellent connections between layers and ability toprint fine features. Intricate solid and hollow parts illustrate theability to combine porous, solid, tortuous, and thin features in asingle printed part to meet the demands of scientists, engineers, anddesigners for various applications.

As shown in the images of FIGS. 2A-2G, the freeform printing methodsdisclosed herein are operable for printing various article structuresusing materials such as acrylonitrile butadiene styrene (ABS; see, e.g.,FIGS. 2A-2E), polyurethane (PU, see, e.g., FIGS. 2H and 2I),polyacrylonitrile (PAN, also known as polyvinyl cyanide, see, e.g.,FIGS. 2J and 2K), acrylics (see, e.g., FIGS. 2F and 2G), and/or othersuitable materials, to form finished articles having wide ranges ofdimensions, complexity, and printing precision. By way of example only,the spiral cone illustrated in FIGS. 2E, 2I, 2K, and 2F, printedaccording to the design of FIG. 2M, represent a precise article printedaccording to an embodiment of the method described herein, the precisearticle having a singular support at the top of the spiral cone fromwhich the arms of the spiral cone extend rotationally. For the sake ofcomparison, a similar spiral cone article (not shown) was 3D printedaccording to a conventional 3D printing method; the conventionallyprinted spiral cone article exhibited inherent mechanical failure pointsalong each arm of the spiral cone, the inherent mechanical failurepoints associated with interfacial weakness between printed layers(leading to cohesive failure, for instance). Such a conventionallyprinted spiral cone article would require multiple (perhaps many)support structures to be printed (e.g., before or concurrent with theprinting of the conventionally printed spiral cone article) to enableadditive printing of the arms of the spiral cone, the trimming of whichwould render the spiral cone article less precise in terms of armdimensions, surface and edge effects, and/or the precision of a pointeddistal portion of each arm. In other words, for the printing of manyarticles, including but not limited to more complex articles or articlesrequiring precise dimensions and shapes, conventional 3D printing istypically disadvantageous, especially when compared to embodiments ofthe method described herein. As such, the methods, e.g., the method 10,disclosed herein typically result in superior article properties andresult in the realization of certain efficiencies during printingassociated with only printing the article and not printing supportstructures. Furthermore, there are efficiencies of post-processingassociated with not having to remove (trim) support structures from the3D printed article. Also, the yield-stress support material (or portionsthereof) may be reusable for subsequent printing of another article inthe yield-stress support bath, which may mean that, unlike conventional3D printing platforms which must be cleaned and any excess printingmedium or build material removed before subsequent printing within or onthe same 3D printing platform, the disclosed apparatuses, yield-stresssupport materials, and yield-stress support baths formed therewith maybe usable for printing multiple articles without, for instance, havingto remove the yield-stress support material from the yield-stresssupport bath.

Referring now to FIG. 3 , a polymer 3D printing method 20 is illustratedthat is configured to enable freeform fabrication of polymericstructures under ambient conditions without the use of printed supportstructures. In some embodiments, the method 20 can include dispensing athermoplastic polymer and solvent solution into a solvent-richyield-stress support bath, at 21. The dispensing 21 can be carried outby any suitable mechanical apparatus such as a syringe, plunger, nozzle,pipe, conduit, pathway, or the like. In some embodiments, the buildmaterial, can be previously dissolved or caused to be dissolved in asuitable solvent to make a viscous polymer solution, which can be loadedinto an ink reservoir for extrusion printing as part of the dispensing21. The polymer solution, during the dispensing 21, can be directlyprinted in (injected into) and supported by the yield-stress supportbath. The yield-stress support bath can comprise a yield-stress supportmaterial configured to maintain particular rheological properties (e.g.,a solid-like state) unless disturbed by a nozzle, such as a printingnozzle, in which the yield-stress support material becomes at leastpartially fluid or has a sufficient mechanical properties (e.g., reducedviscosity) such that the polymer solution can be disposed within thedisturbed portion of the yield-stress support material adjacent to theprinting nozzle.

In some embodiments, the printing nozzle or other mechanical apparatusconfigured to inject or extrude the build material into the solvent-richyield-stress support bath can be fixed or configured to be moved duringthe dispensing 21. For instance, in some embodiments, a computingdevice, e.g., a computer including at least one processor and at leastone memory device, can be configured to move or cause movement of theprinting nozzle between different locations or portions of thesolvent-rich yield-stress support bath. In some embodiments, thecomputing device can move or cause movement of the printing nozzle alonga computer-controlled path or paths while dispensing 21 to formfilaments, layers, and eventually an entire 3D part in the solvent-richyield stress support bath material.

In some embodiments, the printing nozzle can have a longitudinalcontour, form factor, dimensions, and/or surface properties such thatthe use of the printing nozzle to inject, extrude, or otherwise depositthe build material into the solvent-rich yield-stress support bathminimizes the influence of undesirable nozzle movement-induced supportbath liquefaction, which may encourage the up overflow of depositedmaterials. Said another way, the printing nozzle can be dimensioned andconfigured to move through the solvent-rich yield-stress support bathand deposit build material within the yield-stress support bath withoutdisrupting the intra-bath structure and consistency. For example,movement of the printing nozzle through the yield-stress support bathcould, if the printing nozzle is improperly dimensioned and configured,cause a hardening of the yield-stress support bath such that injectionof build material causes the build material simply to overflow theyield-stress support bath and/or travel laterally to the desireddestination volume within the yield-stress support bath. In someembodiments, the printing nozzle can have a sufficiently large length towidth ratio such that movement of the printing nozzle through theyield-stress support bath minimally disrupts the yield-stress propertiesof the yield-stress support bath, thereby not disrupting or onlyminimally disrupting the injection path of the build material upondispensing into the yield-stress support bath.

The yield-stress support material can be or include a yield-stressmaterial based at least in part on a mixture of a solvent andnon-solvent, a single solvent, or a mixture of solvents, which can beselected and formulated to control the speed at which the printed buildmaterial coagulates. The printed part may be still liquid or onlypartially coagulated for some time after dispensing 21, or may remainliquid or only partially coagulated for an extended period of time afterdispensing 21, as shown at 22. Partial coagulation may effectivelyprevent excessive diffusion of printed polymers into the surroundingsupport bath material. While the function of solvent in the yield-stresssupport bath may be to prevent complete coagulation of printed polymers,the function of non-solvent is to initiate the coagulation process.Thus, the type of solvent and non-solvent chosen, as well as the ratioof solvent to non-solvent in the yield-stress support bath can be finelytuned, in light of the material choices and ratio of polymeric buildmaterial and solvent in the printing solution, to achieve the desireddegree of coagulation for the intermediate article. The method 20 canfurther include immersing the yield-stress support bath container in apost-treatment coagulation solution to solidify the printed polymermaterial, at 23. After sufficient time and/or once the finished articleis formed in terms of the degree of coagulation/solidification of thearticle, the finished article can then be removed from the yield-stresssupport material and post-treatment bath, at 24. In some embodiments, nofurther steps or processes or treatments are required after removal ofthe finished article from the yield-stress support bath and thepost-treatment bath in order to achieve a finished article having thedesired dimensions and mechanical properties of the finished printedpart.

For the proposed printing methodology to be feasible, a structure beingprinted should remain liquid or partially liquid to avoid filament/layerinterfaces and nozzle clogging. The printing of a liquid structure isaccomplished by using a yield-stress support bath in which buildmaterial ink is extrusion printed. In general, support bath materialssuitable for 3D printing are thixotropic yield-stress materials whichare also compatible with the solidification/gelation of the printedmaterial. Yield-stress materials behave as solids at rest but as liquidswhen a sufficient shear stress is applied (the yield stress); after thestress is removed, they promptly revert to solid-like behavior. Thus, arigid printing nozzle can easily be inserted into a bulk yield-stresssupport bath. In some embodiments, as the printing nozzle travelsthrough the yield-stress support material in the yield-stress supportbath, it may locally liquefy the yield-stress support material to allowink deposition. In some embodiments, local liquefaction of theyield-stress support material may be helpful or necessary to allow fordeposition of the ink (e.g., polymer build material in solvent and/orother materials) into the yield-stress support material, and suchliquefaction of the yield-stress support material may be caused orcontributed to by the movement of the printing nozzle to or around oradjacent to the desired printing location within the yield-stresssupport bath. However, such liquefaction or a particular extent ofliquefaction of the yield-stress support material, in some embodiments,may be unnecessary and/or undesirable, for reasons including thosedescribed herein related to overflow or upwelling of ink and/or theyield-stress support material. In some embodiments, once the ink (e.g.,solvent solution comprising fluid build material) is injected, dispensedinto, extruded, and/or otherwise disposed within the yield-stresssupport material, the ink (e.g., comprising the fluid build material) isthen trapped in the particular desired location within the yield-stresssupport bath as the yield-stress support material reverts to solid-likebehavior when the printing nozzle travels away from the particulardesired location in which the build material is trapped. In someembodiments, the build material is then trapped in a 3D configurationdefined by a travel path defined for the printing nozzle and may retainits shape even though it is still fluid or partially fluid. An entire 3Dfluid intermediate part can be formed in this way. Then, a stimulus canbe applied which causes or contributes to solidification or partialsolidification of the fluid build material so that it can be separatedfrom the yield-stress support bath as an intact part.

The proposed printing approach may be utilized for any polymer which canbe solubilized and then coagulated to form a continuous solid part. Asnoted above, the concept extends to any solvent-based support bathformulation in which the rheology can be modified to generate ayield-stress material. By way of example only, some embodiments areillustrated and described for which a dimethyl sulfoxide (DMSO)/water(solvent/non-solvent) combination is selected since it is suitable for arange of useful engineering polymers and convenient to handle, howevermany other solvents and non-solvents and combinations thereof weretested, are contemplated, and are within the scope of the currentdisclosure.

Provided below are some, but not all, examples of methods for freeform3D printing of various polymeric articles, similar to or according tothe methods 10 and 20 described hereinabove.

For instance, according to one example ink formulations were prepared bydissolving a solid polymer in a solvent, e.g., DMSO (Bioreagent grade,Fisher, Fair Lawn, NJ, USA). In some embodiments, in order to 3D printpolyurethane (PU) parts, 3.0 g of soft thermoplastic polyurethane(Elastollan soft 35A, BASF, Wyandotte, MI, USA) were mixed with 7.0 mLof DMSO to make nominally 30.0% w/v ink; 10.0% w/v and 20.0% w/v inkswere prepared by combining 1.0 g or 2.0 g PU with 9.0 mL or 8.0 mL DMSO,respectively. In some embodiments, to prepare a PAN ink, PAN(poly(acrylonitrile), 150 kDa, Pfaltz and Bauer, Waterbury, CT, USA) wasdissolved in DMSO at a concentration of 7.6% w/w or 15.2% w/w. In someembodiments, to prepare an ABS ink, ABS filament was dissolved in DMSOto make 30.0% w/w ABS ink. According to one or more embodiments, anacrylic support material filament (P400-SR, Stratasys, Eden Prairie, MN,USA) was dissolved in DMSO to make a 33.3% w/w ink.

According to one or more embodiments, to prepare 50 mL of 1.5% Carbopolsupport bath material in 9:1 DMSO:H2O, 45 mL DMSO was mixed with 5 mLdeionized water before adding 0.75 g Carbopol 940 (Lubrizol, Cleveland,OH, USA) and mixing thoroughly. According to some embodiments, theresulting mixtures was allowed to equilibrate for at least 12 hoursbefore use. According to some embodiments, after confirming at leastadequate performance, the formulations were used without pH adjustment.In some embodiments, 1.0%, 2.0%, and 2.5% Carbopol formulations, amongother possible formulations, were prepared in a similar fashion. In someembodiments, the solvent ratio was also varied from 0-15% v/v water.

According to some embodiments, Laponite XLG (BYK Additives Inc.,Gonzales, TX)) was dispersed in DMSO and water was then added to reach afinal composition of 3:1 DMSO:H₂O (v:v) with 3% Laponite XLG (w/v). Insome embodiments, the yield-stress support material was then mixed(e.g., vortexed) thoroughly and allowed to stand for some time (e.g., 12hours or more) before printing.

In some embodiments, printing was carried out using a Hyrel Engine SR(Hyrel3D, Norcross, GA) with a CSD-5 dispensing head (without a UVarray) controlled with a Repetrel software interface. Ink, preparedaccording to any of the embodiments of compositions, apparatuses,processes, and/or methods described herein, was loaded in a disposable 5mL syringe fitted with a stainless steel 23 gauge tip (Norsdon EFD,Vilters, Switzerland). According to some embodiments, STL models weresliced using an embedded Slic3r utility in the Repetrel software togenerate G-code. According to some embodiments, parameters for additivemanufacturing using the apparatuses described herein can comprise alayer thickness of about 0.15 mm and a printing speed of about 600mm/min.

According to some embodiments, after printing, the entire support bathwas immersed in water for at least 3 hours to replace the solvent in theyield-stress support bath (e.g., DMSO) with non-solvent (e.g., H₂O) andtherefore coagulate the printed polymer (e.g., ABS, PU, or the like)within the yield-stress support bath. According to some embodiments,once some, most, or all of the solvent is replaced, the solid printedparts were removed from the yield-stress support material and rinsed(e.g., with water, deionized (DI) water, tap water, or the like) toremove any excess yield-stress support material from the surface of theprinted article. In some embodiments, deionized water containing 1% w/vsodium chloride (Sigma Life Sciences, St. Louis, MO, USA) or 5% sodiumchloride was used instead of pure DI or tap water.

According to some embodiments, rheological properties were measuredusing a rheometer (MCR-702 TwinDrive, Anton-Paar, Graz, Austria) with a25 mm sandblasted (Ra=4:75 μm) parallel-plate measuring geometry, 1 mmgap. In some embodiments, to determine the yield stress quantitatively,steady rate sweeps were conducted by varying the shear rate from 100/sto 0.01/s, and the stresses were measured at different shear rates; apre-shear step at 100/s for 30 sec followed by a 1 min rest to recoverstructure was used to eliminate loading effects.

Printing Results

Printed structures using a variety of ink and support materialformulations are shown in FIGS. 2A-2K along with the designs in FIGS.2L-2N according to which the printed structures were printed. Ingeneral, the printed parts closely match the original design, regardlessof the build material. For each material, ink concentration, supportbath material formulation, and print parameters were optimized for bestresults; material details are discussed in the following sections. Wallthickness was on the order of about 300 μm, which was approximatelyequivalent to the extrusion tip width.

As illustrated, printed ABS structures demonstrate a variety of featuretypes: thin walls, flat overhangs, solid regions, and detailed surfaces.The gear vase and tubular structures illustrate the ability to printfunctional containers and conduits with arbitrary features otherwiseunachievable by additive manufacturing such as the perfectly horizontalupper section of the T-junction. Attempting to form structures having asimilar form factor using FDM would require a more complex printingprocess and would result in a formed article that is mechanically andstructurally deficient. For instance, to print structures having asimilar form factor using FDM would require the part and/or the entireprinting platform be rotated in space during printing, resulting in amore complex printing process, requiring more complex parts sinceanalogous features may not have an ‘easy’ orientation for 3D printingaccording to FDM. In contrast, using a yield-stress support bathaccording to any of the embodiments described herein, the print qualityis nearly independent of orientation of the printed article and resultsin more accurate and precise printing of the article relative to theinput model. Also, the thin walls of the tube which might deform duringFDM were substantially unaffected by gravity during support bath-enabledprinting, which may be due to the fact that strain is prevented, for theintermediate article and/or the finished article, by the yield-stresssupport material surrounding the printed intermediate article and/orfinished article.

Because the coagulation of the printed material often requires diffusionbetween the yield-stress support bath and the printed material, thinwalled parts or shells such as the tubular conduit and hollow vasestructures are sometimes most convenient to print using the describedprocesses according to some embodiments. However, in some embodiments,such as illustrated in FIG. 2B, bulk solid parts are also achievableusing the described approaches. Blocks having dimensions of, forinstance, 8×8×6 mm were printed (see, e.g., FIG. 2B) as a test case todetermine parameters and verify that they can be fabricated, howeverother bulk and solid parts and structures were also successfully printedand many others were contemplated and are covered by the presentdisclosure. The coagulation process for material within the bulk part iscomplicated by the presence of the coagulated shell around the exterior.This prevents shrinkage of the overall shape as solvent slowly diffusesout of the interior leaving behind coagulated solid build material. Insome cases, the volumetric shrinkage is accommodated by the formation ofvoid space within the bulk part, as discussed in more detail in thefollowing section. A more controllable option is to reduce the printspeed so that the interior layers almost completely coagulate as thenext layer is being printed. This ensures that the entire volume of theprinted part experiences similar coagulation conditions and minimizesthe occurrence of voids in printed parts.

In general, similar shape fidelity is achieved for all materials andstructures. Differences in performance for specific build materials arediscussed in relation to ink formulations and support materialformulations in later sections.

Morphology and Mechanical Property Results

The porosity of solid printed ABS parts was evaluated by opticalmicroscopy, as shown in FIG. 4 . With optimized printing conditions anddesigns, nominally solid ABS parts have a porosity of about 15% byvolume; voids are typically in the form of spherical cavities and areattributed to pockets of fluid which form as the polymer coagulates andshrinks after printing.

As illustrated in FIG. 5 , printed ABS tensile test specimens arecompared with conventional FDM tensile test specimens; ABS was selectedsince the build material is identical for both processes. Although thematerials are identical, the mechanical behavior of printed specimensshows some variations and printed specimens are less stiff than the FDMparts and reported intrinsic properties of ABS.

Material Selection Results

A variety of factors affect the material coagulation process. Wetspinning studies of PAN have shown that the bath compositionsignificantly affects the diffusion of both DMSO and water; this holdstrue to a greater or lesser degree with any polymer/solvent/non-solventsystem. It can be explained in terms of two competing effects: theformation of a solid surface layer on the extruded polymer solutionwhich serves as a barrier to further solvent exchange, and the solventgradient existing between the polymer solution and the coagulation bath,which provides the driving force for coagulation. In solvent-richcoagulation baths, the surface barrier against solvent exchange is verythin so solvent exchange proceeds rapidly. As the water contentincreases, the solvent exchange slows since the barrier layer becomesthicker. However, the driving force for solvent exchange is alsoincreasing and eventually dominates the process. It is noteworthy thatthe different coagulation conditions are also associated with differentfiber morphologies: water-rich coagulation baths result in fibers withstrictly circular cross sections (due to the rapid coagulation at thespinneret surface) but often with large irregular internal voids, whilesolvent-rich coagulation conditions generally result in fully densebean-shaped cross-sections since the outer shell is soft enough tocollapse as solvent exchange progresses. In this work, a fully denseinternal morphology along with slow coagulation to permit fusion ofadjacent filaments is desirable, so the focus is on solvent-richconditions. The specific effects of variation in ink and/or solventformulation are discussed in the following sections.

After printing is complete, the part must be completely solidified forrecovery from the yield-stress support bath and subsequent utilization.In some ways, this is analogous to the polymer fiber wet spinningprocess in which a polymer solution is extruded through a spinneret intoa solvent-rich coagulation bath to form the initial fiber, then passesthrough solvent-poor stages to complete solidification. However, in theprinting process disclosed herein, the yield-stress support materialmight not be replaced without damaging the printed liquid (or partiallycoagulated) part. Instead, the entire support bath is immersed in alarge volume of non-solvent so that the overall solvent concentration issignificantly reduced. In some embodiments, over time, the largereservoir of non-solvent draws solvent out of the yield-stress supportbath to approach a homogeneous solvent-poor composition throughout theyield-stress support bath volume. In turn, this solvent-poor environmentdraws residual solvent out of the printed liquid or partially coagulatedpolymer structure, leaving a solid part.

For fiber spinning processes, the solvent composition is typically20-70% (with the remainder being a non-solvent). However, since the goalin this work is slow solidification rather than near-instantaneousstabilization of rapidly forming fibers, a higher solvent content isexpected to produce better results. In polymer processing, mostinteractions are governed by entropy. The compositional entropy enabledby solvent/non-solvent mixing may be far greater than the loss due topolymer solidification, so a polymer solution solidifies on contact witha bulk solvent/non-solvent mixture compatible with the solvent butincompatible with the polymer. Without wishing to be bound by anyparticular theory, the solvent may diffuse into the solution, increasingthe overall entropy. However, without wishing to be bound by anyparticular theory, because the non-solvent properties dominate in theresulting mixture of solvent and non-solvent, the polymer may no longerbe soluble and may form a solid mass.

In some embodiments, criteria for selecting a solvent/non-solvent pairfor processing a polymer using the proposed printing process may includeone or more of at least: the solvent/non-solvent pair should bemiscible, the solvent should produce polymer solutions with suitableproperties (viscosity, stability), and the polymer should be essentiallyinsoluble in the non-solvent. To demonstrate this process, DMSO was usedas the solvent and water as the non-solvent. This combination ismiscible in all proportions, and DMSO is an effective solvent for a widearray of polymers, enabling testing of a variety of build materials withthe same support bath material system. DMSO is also convenient anddesirable at least because it is relatively non-volatile, minimizingsolvent loss to the atmosphere and concomitant alteration of thesolvent/non-solvent ratio in the yield-stress support material. Inaddition, commercially available rheology modifiers are available toconvert the free flowing DMSO/water mixtures to yield-stress materials.However, the process may be implemented with any combination of solventand non-solvent for which the rheology can be appropriately adjusted.

Ink Formulation Results

The ink formulation affects the fabrication process in various ways.There are at least two stages to the process: deposition andcoagulation. During deposition, the viscosity and viscoelasticity of theink affect shape fidelity, achievable speed, and overall flow behavior.During coagulation, the ink formulation affects coagulation speed, sizeand morphology of filaments/parts, and final properties of the printedpart. Print parameters and ink formulations are designed to minimizevariations due to the deposition process

Ink formulations should balance printability with printed part quality.In some embodiments, a lower polymer concentration in the inkformulation may make flow control easier, to a point; however, filamentsformed by low-concentration inks may be inconsistent and shrinksignificantly relative to the printed design. Shrinkage is particularlytroublesome since it may cause separation between adjacent filamentsduring the coagulation process as well as distort the overall shape. Inextreme cases, the material will simply form disconnected wisps of solidmaterial instead of a continuous filament. On the other hand, highlyviscous polymer-rich ink formulations are more difficult to printaccurately due to a tendency to ooze and failure to start/stop cleanly.

In general, structures printed with higher ink concentrations are morerobust; this makes sense since more polymer is deposited in concentratedinks than in dilute inks. However, the ranges for ‘dilute’ and‘concentrated’ inks varies from polymer to polymer; high molecularweight PAN (150 kDa) is printable in the 7-15% w/v range, while ABS,acrylic, and soft PU are printable in the 10-30% range. Thesedifferences are a result of specific polymer properties as well as theirinteractions with solvent and non-solvent during the printing andpost-processing steps. Although the specified ranges are printable, theoutcome may vary significantly. For instance, as illustrated in FIG. 6A,a build material comprising 10% PU produces recognizable parts but thereare often gaps due to the small amount of deposited polymer andstructures collapse under their own weight in air. On the other hand, asillustrated in FIG. 6B, a build material comprising 30% PU producesrelatively softer, more robust, more continuous parts which can supporttheir own weight in air. Similarly, as illustrated in FIGS. 6C and 6D,both 20% and 30% ABS ink formulations may produce parts that are orappear solid; however, the 20% build material in FIG. 6C results inweaker structures since less material is deposited, while the 35% ABSbuild material in FIG. 6D produces distinctly thicker walls, and is muchmore difficult to control. As such, the conveniently printable range ofconcentrations for ABS using these printing conditions, e.g., up to 30%and 35% ink, may be more useful or only useful for a limited range ofpart morphologies where dispensing start/stop behavior is not critical.The macroscopic features of printed PAN parts are less sensitive topolymer concentration in the range used herein, but its coagulationbehavior presents other challenges.

Without wishing to be bound by any particular theory, one of thesignificant factors affecting ink coagulation is the identity of thepolymer. For a given polymer, the coagulation behavior is relativelyinsensitive to the actual polymer content. However, for instance, lowerconcentration formulations may take slightly longer to coagulatecompletely and may develop gaps due to shrinkage, while the printedmaterial after coagulation looks and feels similar regardless of the inkconcentration.

As illustrated in FIGS. 6C and 6D, printed ABS may form more rigid solidparts than PU, as illustrated in FIGS. 6A and 6B, regardless of the inkconcentration. Observations indicate that solvent diffusion duringcoagulation was nearly unidirectional: printed parts have uniform hardsurfaces and closely match the designed dimensions. This indicates thatwater was not incorporated into the printed build material duringcoagulation and that ABS coagulation is a relatively simple process ofDMSO diffusing to the surrounding support bath, not a bidirectionalprocess with water diffusing into the printed material as well as DMSOdiffusing out. Similar results are observed for acrylic and PU buildmaterials: the printed parts are rigid solids which retain their shapein air and show no evidence of support bath material surface inclusionsor trapped solvent. The behavior of PAN, however, is quite different andis discussed in more detail in relation to PU.

Although PU is less compatible with water than PAN, the kinetics of thesolvent diffusion process differ between polymers. PU coagulatesrelatively slowly over a wide range of support bath solvent compositions(about 5%-25% water), producing similar structures regardless of theexact support bath composition. Without wishing to be bound by anyparticular theory, this may be attributed to the relatively weakinteractions between PU and water, which may lead to almostunidirectional diffusion of solvent out of the printed material (ratherthan a complex solvent exchange process where water diffuses into theprinted material as DMSO diffuses out). Without wishing to be bound byany particular theory, this diffusion process may be primarilycontrolled by polymer content, although the composition of theyield-stress support bath may determine the strength of the drivingforce and there is therefore also an observable difference incoagulation speed depending on the yield-stress support materialformulation.

In contrast, PAN often requires more extensive process optimization. Insome embodiments, PAN-based ink formulations may be sensitive to thewater content of the yield-stress support material. For instance, insome embodiments, for support bath materials above 15% water, the inkcoagulates almost immediately after extrusion (or as a trailing blobattached to the extrusion tip), making it very difficult to preciselycontrol the process. Indeed, printing PAN structures in LaponiteXLG-based support bath material (25% water) often requires extensivemanual intervention to clear away initial dragging artifacts but may bemore successful when the extrusion is continuous. In some embodiments,printed PAN parts are often incomplete or distorted due to these orother issues. As such, PAN printing in Laponite XLG may be limited toprinting simple parts which can be printed without interruption. On theother hand, in more DMSO-rich Carbopol based support bath material,coagulation may be much slower, which may facilitate the depositionprocess but often causes a deterioration in part quality. Becausecoagulation is retarded in DMSO-rich Carbopol support bath formulations,diffusion of the printed polymer into the surrounding support bathmaterial often becomes significant and the properties of the printedparts are noticeably different. As such, instead of hard, rigidfeatures, PAN parts printed in Carbopol as described for PU are flexibleand slippery due to incorporation of Carbopol and water in thecoagulating polymer. In some embodiments, this traps solvent and changesthe mechanical properties of the printed part. Although the solvent canbe removed by drying, the weakened diffuse polymer network is unable toretain the designed shape and generally collapses. In addition, even ifthe printed part retains its shape upon drying, it remains prone toabsorbing water again, making its properties unpredictable. Thus, thesimple aqueous post treatment suitable for recovering useable PU partsmay be inadequate for PAN.

Several strategies to simultaneously improve PAN printability andstructural integrity were tested. Replacing water with ethanol in boththe yield-stress support material formulation and the post-treatmentstep had little effect on the outcome, although ethanol was expected tobe more effective at coagulating PAN based at least in part on reportedinteraction parameters. Chilling the entire system during post-treatmentalso had little effect, despite the expectation that it would retardpolymer diffusion more significantly than solvent exchange. Heattreatment within the yield-stress support bath after printing (e.g., byheating for 1 hr at 85° C.) caused deterioration in part qualitycompared to ambient post-processing: the printed parts were intact butunable to support their own weight in air.

Support Material Formulation Results

To enable solvent-based ink formulations and the formation of fluid 3Dparts, compatible support bath materials were developed. Support-bathenabled fabrication for a variety of processes may rely on fluidprecursors, although work to date has focused on cross-linkable materialsystems where the entire volume of the ink material is transformed intoa solid or gel part. In some embodiments, solvent-based ink formulationswere developed which coagulate to form solid printed parts. Support bathmaterials may comprise a solvent (or mixture of solvents) and a rheologymodifier. In some embodiments, the solvent chosen may dictate many ofthe chemical interactions with printed build material while the rheologymodifier is, ideally, an inert additive which transforms the fluidsolvent into a yield-stress material. In some embodiments, the polymerbuild material is pre-polymerized, meaning the stimulus to causecoagulation is simply removal of the solvent. Thus, the yield-stresssupport bath must be formulated to promote slow coagulation of theprinted part by diffusion of solvent into the yield-stress supportmaterial. As has been demonstrated for other build materials where thecoagulation stimulus is distributed throughout the yield-stress supportbath, speedy coagulation often results in nozzle clogging, whileinsufficient coagulation speed results in poorly-defined parts. That is,where ink and support bath materials are miscible, diffusion at theinterface causes slow deterioration of print quality. For consistentprint quality, the yield-stress support bath according to someembodiments promotes at least some degree of coagulation so that partquality is independent of printing time. In some embodiments,coagulation is promoted by using a combination of a good solvent (hereindimethyl sulfoxide (DMSO), the same solvent as the ink formulation) anda poor solvent or non-solvent (water) to control the coagulation processin conjunction with a commercially available rheology modifier which iscompatible with these mixed solvents. Since the kinetics of thecoagulation process are specific to ink formulations and, to a lesserdegree, to part designs, a support bath with tunable solvent content isdesirable for solution-based polymer printing.

In some embodiments, Carbopol can be used as a rheology modifier tocontrol support bath rheology. In some embodiments, Carbopol was shownto be particularly useful for the DMSO-water solvent-non-solvent systemsince it works equally effectively to thicken any combination of thesetwo liquids. This is clearly visible in the rheological properties ofthe formulations at each end of the solvent spectrum (pure DMSO and purewater), which can be similar at least in some instances. Carbopolconsists of cross-linked poly(acrylic acid) particles which may swell inwater and other solvents to form microgels. When these microgels occupythe entire volume of the solvent, they are jammed together resulting inyield-stress behavior. While Laponite XLG can also modify the rheologyof some formulations, in some embodiments Laponite XLG may require asignificant amount of hydrogen bonding with the solvent to be effectiveand is therefore limited to DMSO-water formulations containing at least25% water. Laponite XLG is discussed herein as an alternativerheological additive to demonstrate that the solvent-enabled supportbath printing approach is not limited to microgel-based rheologicaladditives such as Carbopol. Furthermore, other rheological additives arealso possible for providing suitable mechanical properties forsupporting printing using solvent-based ink formulations.

Without wishing to be bound by any particular theory, the solventcomposition of the yield-stress support bath may determine the strengthof the driving force for solvent diffusion and therefore the speed atwhich printed parts coagulate, while the concentration of the rheologymodifier (Carbopol, Laponite, etc.) may determine the overall rheologyof the yield-stress support material and influences print quality. Insome embodiments, a higher concentration of rheological additive mayresult in a higher yield stress for a support bath formulation. In someembodiments, the preparation protocol may be critical for Carbopol; forinstance, the solvents may be pre-mixed or combined with the dryCarbopol at the same time. Pre-mixing DMSO with Carbopol, then addingwater later, resulted in more rapid coagulation of the printed materialand therefore reduced print quality. Without wishing to be bound by anyparticular theory, this may be attributed to a higher water fraction inthe interstitial solvent between microgels since the microgels initiallyswelled in pure DMSO. In other words, delaying the addition of water tothe formulation may have the same effect as increasing the overall waterconcentration, that is, coagulation of the printed ink material may befaster.

Although the solvent composition, according to some embodiments, may becritical for achieving sufficient printing performance, it sometimes oroften has little effect on the rheology and/or other properties of theyield-stress support material. For instance, a concentration of 1.5%Carbopol 940 in 100% water is quite similar to a concentration of 1.5%Carbopol 940 in 100% DMSO. This may be a valuable feature of the type ofmulti-component support bath material system described herein. Withoutwishing to be bound by any particular theory, as intermediate solventformulations show, the rheology may be independent of or nearlyindependent of the solvent composition. As such, in some embodiments,the essential rheological behavior to effectively support the printingprocess can be adjusted independently of the solvent composition, whichcontrols coagulation and vice-versa.

In an example in which the building material comprises ABS, aconcentration of about 90% DMSO is found to be sufficient for printingstructures. This solvent content induces reasonably rapid hardening ofthe deposited filaments and is rich enough in solvent that there is adelay between deposition and full solidification. In other words, thereis sufficient solvent in the ABS/DMSO solution such that it takes asufficiently long time for the DMSO to be removed and for the ABS tosolidify, forming the finished article. This behavior rapidly stabilizesthe printed structure but avoids issues with nozzle clogging due torapid coagulation. With lower solvent content (e.g., less than or equalto about 85%, as illustrated in FIGS. 7A and 7B), dragging is observedas the filament coagulates too rapidly and sticks to the extrusion tip.On the other hand, building materials comprising ABS in 95% DMSO, forinstance, results in a coagulation process that is slow andinconsistent, resulting in intermittent dragging and smearing of printedparts. The resulting poor shape fidelity is illustrated by the spiralcone parts shown in FIGS. 7C and 7D.

In some embodiments, a building material can comprise PU ink. Withoutwishing to be bound by any particular theory, for PU/solvent buildingmaterials, the main determinant of structure quality may be the rheologyof the yield-stress support material. As such, in some embodiments,processes using PU ink may be relatively insensitive to the solventcomposition since it inherently coagulates more slowly than PAN or ABS.In a support bath material with a high yield stress, the flow of theyield-stress support material behind the extrusion tip is slower than ina support bath material with a lower yield stress (more prone tofluid-like behavior). Thus, with a low-viscosity ink in a highyield-stress support material, backflow behind the extrusion tip can beproblematic. As such, this may result in a loss of shape fidelity due touncontrolled upward deformation of filaments in a Z direction (e.g.,depth direction) during printing. Without wishing to be bound by anyparticular theory, a support bath material with low yield stress mayimprove print quality. In some embodiments, it may also be moreeconomical and may facilitate the solvent exchange process for finalcoagulation of the printed material. As illustrated, results may bereasonably similar for support bath material formulations with up toabout 90% DMSO, with up to about 95%, and with up to about 100% DMSOcontent in the yield-stress support material. However, in someembodiments, the quality of the printed parts may deteriorate becausethe driving force for coagulation is so weak that polymer diffusionbecomes significant. In some embodiments, a disadvantage of lowyield-stress support material is a propensity to distortion if theyield-stress support bath is jarred during and/or after printing. Forinstance, jostling can cause bulk motion of the yield-stress supportmaterial within the container, distorting all or part of the printedmaterial. Depending on the specific printer configuration, thisconsideration may limit the speed of the print head and affect theoverall fabrication time.

While PAN parts are successfully fabricated using this methodology,PAN-based ink may be more sensitive to the yield-stress support materialcomposition. When printed in relatively water-rich support bathmaterial, PAN ink coagulates so quickly that printing is complicated bydragging of the coagulated material. On the other hand, in a moresolvent-rich support bath material, as the coagulation process slows,other processes, such as diffusion of the polymer itself into thesurrounding support bath material, may become significant. Thus, insolvent-rich support bath materials, shape fidelity may suffer and PANparts may become soft due to high porosity and solvent content. In someembodiments, when water is omitted from the yield-stress supportmaterial, defined shapes may not be recovered due to extensive diffusionof the printed material within the yield-stress support bath. At theopposite extreme, when a fully aqueous support bath material isutilized, the printed ink may coagulate quickly, e.g., immediately uponcontact with the yield-stress support material and may adhere to or clogthe tip instead of being deposited in the designed sequence of filamentsand layers.

Post-Treatment Results

An important feature of the support-bath enabled printing methodology isthe ability to form structures from fluid build materials. However, thisalso presents a problem: fluid structures only retain their shape solong as they are undisturbed in the yield-stress support bath. To be ofpractical use, it is essential that the fluid part be converted to asolid which can be removed from the yield-stress support bath. As notedabove, in solvent-enabled printing, the stimulus for this transition isthe loss of solvent as it diffuses from the printed material to thesurrounding support bath material. Without wishing to be bound by anyparticular theory, in a solvent-rich support bath formulation, thedriving force for this diffusion may be weak and coagulation maytherefore be slow. Thus, a post-treatment step may be introduced toincrease the driving force for coagulation by increasing the non-solventcontent in the material surrounding the printed part. In other words,after printing, the yield-stress support bath can be immersed in alarger reservoir filled with water or an aqueous salt solution (or anyother suitable solution operable to diffuse the solvent) to reduce theoverall solvent content and drive coagulation of the printed parts.

For ABS, PAN, and acrylic parts, among others, the post-printingimmersion in water is helpful or essential to achieve solid parts in areasonable time frame. Although ABS and PAN inks slowly coagulate in 90%DMSO, they remain relatively soft at this high solvent content. In someembodiments, acrylic ink visibly changes from transparent brown toopaque beige during coagulation. However, no visual evidence ofcoagulation is observed before immersion in the post-treatment bath,suggesting that the post-treatment is essential for diffusion of thesolvent and coagulation of the polymeric material.

For PU, a visible change is also evident as the transparent ink forms awhite solid. In support bath materials with up to about 90% DMSO,visible progress towards coagulation is apparent within 30 min withoutpost-treatment. However, printed PU structures approach equilibrium withthe yield-stress support bath at a relatively high residual solventlevel since the yield-stress support bath is solvent-rich even though itinitiates the coagulation process for the ink. Therefore, afterprinting, a more aggressive treatment to remove residual solvent can becarried out to make the printed part solid rather than simply a veryplastic polymer paste, which is prone to deformation if removed from theyield-stress support bath as shown in FIG. 8 . In some embodiments, theyield-stress support material water content may be insufficient tocompletely solidify the printed material and further treatment may behelpful or essential for PU coagulation. In some embodiments, simplyimmersing the yield-stress support bath containing the printed part inadditional water may be sufficient to partially or completely coagulatethe printed structures into robust freestanding parts.

CONCLUSIONS

Disclosed herein are various embodiments of a method for polymer 3Dprinting that enables freeform fabrication of polymeric structures underambient conditions without the use of printed support structures. Insome embodiments, the build material is first dissolved in a suitablesolvent for extrusion printing. In some embodiments, the polymersolution is then directly printed in and supported by a yield-stresssupport bath to form filaments, layers, and eventually an entire 3D partin the yield-stress support material. In some embodiments, the printedpart may remain a liquid, such as a viscous liquid, or an only partiallycoagulated material. According to some embodiments, after printing, theyield-stress support bath container may be immersed in a post-treatmentcoagulation solution to partially or fully solidify the printed polymermaterial, and the printed part may then be removed from the yield-stresssupport material and post-treatment bath. Provided herein aresolvent-rich support bath materials that enable facile 3D fabrication ofa range of polymeric build materials at room temperature. Printingperformance can be adjusted by varying the ink and support bathformulations to achieve desired resolution, printing speed, and surfacequality. Post-treatment is an essentially hands-off procedure for thisapproach. The advantages of the disclosed methods, apparatuses andmaterials of manufacture, some of which are outlined throughout thisdisclosure, provide a compelling and effective solution to many of theproblems in the 3D printing industry, some of which are outlined earlierin the disclosure.

Described hereinabove are methods and associated apparatuses for forminga yield-stress support material, preparing a yield-stress support bathcomprising the yield-stress support material, preparing a build materialsolution for 3D printing into the yield-stress support material, formingan intermediate article within the yield-stress support material, andexposing the intermediate article to a stimulus (e.g., a chemicaloperable to remove the solvent from the build material solution) tosolidify or partially solidify the intermediate article to form afinished article.

In some embodiments, a method was provided for 3D printing of a finishedarticle, the method comprising: dispensing a mixture of a polymericmaterial and a solvent into a yield-stress support bath; allowing themixture to only partially coagulate, forming an intermediate article;and exposing the intermediate article to a post-treatment coagulationsolution to fully solidify the intermediate part, forming the finishedarticle. In some embodiments, the method can further comprise dissolvingthe polymeric material in the solvent to form the mixture of thepolymeric material and the solvent. In some embodiments, the polymericmaterial can be a first polymeric material and the solvent is a firstsolvent. In some embodiments, the method can further comprise: mixing arheological additive material with a second solvent, a mixture ofsolvents, and/or a solvent/non-solvent mixture, any of which can includethe first solvent; and allowing the mixture of the rheological additivematerial with a second solvent, a mixture of solvents, and/or asolvent/non-solvent mixture to become at least partially solid-like,forming the yield-stress support bath. In some embodiments, at least oneof the dispensing, the allowing, or the exposing can be carried out byan apparatus comprising a reservoir configured to contain a supply ofthe mixture of the polymeric material and the solvent, a nozzle, and acomputing device. In some embodiments, the nozzle may be configured anddimensioned to reduce or eliminate nozzle movement-induced liquefactionof the yield-stress support bath. In some embodiments, the apparatus canbe configured to communicate the mixture of the polymeric material andthe solvent from the reservoir, through the nozzle, and into theyield-stress support bath. In some embodiments, the computing device canbe configured to move the nozzle during the dispensing such that a firstportion of the supply of the mixture of the polymeric material and thesolvent can be dispensed in a first portion of the yield-stress supportbath and a second portion of the supply of the mixture of the polymericmaterial and the solvent can be dispensed in a second portion of theyield-stress support bath. In some embodiments, the 3D printing can becarried out at about room temperature. In some embodiments, theintermediate article and finished article can be formed free of printedsupport structures. Said another way, whereas other 3D printingtechniques often require a support structure to be concurrently printedwith the finished article to help support the article during printing,the methods and associated apparatuses described herein may not use anysupport structures or may use less support structures than othermethods.

According to another embodiment, as described hereinabove, a method isprovided for 3D printing of a finished article, the method comprising:dissolving a polymeric material in a solvent to form a mixture of thepolymeric material and the solvent; dispensing the mixture of thepolymeric material and the solvent into a yield-stress support bath;allowing the mixture to only partially coagulate, forming anintermediate article; and exposing the intermediate article to apost-treatment coagulation solution or alternative solidificationstimuli (such as radiation and/or temperature change) to fully solidifythe intermediate part, forming the finished article. In someembodiments, the polymeric material may be a first polymeric materialand the solvent may be a first solvent. In some embodiments, the methodcan further comprise: mixing a rheological additive material with asecond solvent, a mixture of solvents, and/or a solvent/non-solventmixture, any of which can include the first solvent; and allowing themixture of the rheological additive material with a second solvent, amixture of solvents, and/or a solvent/non-solvent mixture to become atleast partially solid-like, forming the yield-stress support bath. Insome embodiments, the dispensing may be carried out by an apparatuscomprising a reservoir configured to contain a supply of the mixture ofthe polymeric material and the solvent, a nozzle, and a computingdevice, the apparatus configured to carry out at least one of thedispensing, the allowing, and the exposing. In some embodiments, theapparatus can be configured to communicate the mixture of the polymericmaterial and the solvent from the reservoir, through the nozzle, andinto the yield-stress support bath. In some embodiments, the computingdevice may be configured to guide the movement the nozzle during thedispensing such that a first portion of the supply of the mixture of thepolymeric material and the solvent can be dispensed in a first portionof the yield-stress support bath and a second portion of the supply ofthe mixture of the polymeric material and the solvent can be dispensedin a second portion of the yield-stress support bath. In someembodiments, the nozzle may be a printing nozzle. In some embodiments,the 3D printing is carried out at about room temperature. In someembodiments, the intermediate article and finished article may be formedfree of printed support structures.

According to still other embodiments, a method is provided, as describedhereinabove, for forming a yield-stress support bath forthree-dimensional printing of a finished article, the method comprising:mixing a rheological additive material with a solvent, a mixture ofsolvents, and/or a solvent/non-solvent mixture to form a supportmixture; and allowing the mixture of the rheological additive, solvent,mixture of solvents, and/or solvent/nonsolvent mixture to become atleast partially solid. In some embodiments, the solvent may be a firstsolvent. In some embodiments, the method may further comprise: mixing apolymeric material and a second solvent to form a print mixture;disposing said print mixture into a bath of the support mixture;allowing the printing mixture to only partially coagulate, forming anintermediate article; and exposing the intermediate article to a posttreatment coagulation solution to fully solidify the intermediate part,forming the finished article. In some embodiments, 3D printing may becarried out at about room temperature, and/or the intermediate articleand finished article may be formed free of printed support structures.In some embodiments, the polymeric material may be a first polymericmaterial and the solvent may be a first solvent. In some embodiments,the method can further comprise: mixing a rheological additive materialwith a second solvent, a mixture of solvents, and/or asolvent/non-solvent mixture, any of which can include the first solvent;and allowing the mixture of the rheological additive material with asecond solvent, a mixture of solvents, and/or a solvent/non-solventmixture to become at least partially solid-like, forming theyield-stress support bath. In some embodiments, at least one of thedispensing, the allowing, and the exposing can be carried out by anapparatus comprising a reservoir configured to contain a supply of themixture of the polymeric material and the solvent, a nozzle, and/or acomputing device. In some embodiments, the apparatus may be configuredto communicate the mixture of the polymeric material and the solventfrom the reservoir, through the nozzle, and into the yield-stresssupport bath. In some embodiments, the computing device may beconfigured to move the nozzle during the dispensing such that a firstportion of the supply of the mixture of the polymeric material and thesolvent can be dispensed in a first portion of the yield-stress supportbath and a second portion of the supply of the mixture of the polymericmaterial and the solvent can be dispensed in a second portion of theyield-stress support bath.

In some embodiments, one or more of the operations, steps, elements, orprocesses described herein may be modified or further amplified asdescribed below. Moreover, in some embodiments, additional optionaloperations may also be included. It should be appreciated that each ofthe modifications, optional additions, and/or amplifications describedherein may be included with the operations previously described herein,either alone or in combination, with any others from among the featuresdescribed herein.

The provided method description, illustrations, and process flowdiagrams are provided merely as illustrative examples and are notintended to require or imply that the steps of the various embodimentsmust each or all be performed and/or should be performed in the orderpresented or described. As will be appreciated by one of skill in theart, the order of steps in some or all of the embodiments described maybe performed in any order. Words such as “thereafter,” “then,” “next,”etc. are not intended to limit the order of the steps; these words aresimply used to guide the reader through the description of the methods.Further, any reference to claim elements in the singular, for example,using the articles “a,” “an,” or “the” is not to be construed aslimiting the element to the singular. Further, any reference todispensing, disposing, depositing, dispersing, conveying, injecting,inserting, communicating, and other such terms of art are not to beconstrued as limiting the element to any particular means or method orapparatus or system, and is taken to mean conveying the material withinthe receiving vessel, solution, conduit, or the like by way of anysuitable method.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of teachings presented in theforegoing descriptions and the associated drawings. Although the figuresonly show certain components of the apparatus and systems describedherein, it is understood that various other components may be used inconjunction with the system. Therefore, it is to be understood that theinventions are not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Moreover, the steps in themethod described above may not necessarily occur in the order depictedin the accompanying diagrams, and in some cases one or more of the stepsdepicted may occur substantially simultaneously, or additional steps maybe involved. Although specific terms are employed herein, they are usedin a generic and descriptive sense only and not for purposes oflimitation. Specific equipment and materials described in the examplesare for illustration only and not for purposes of limitation. Forinstance, any and all articles, portions of articles, structures, bulkmaterials, and/or the like, having any form factor, scale, dimensions,aesthetic attributes, material properties, internal structures, and/ormechanical properties, which are formed according to any of thedisclosed methods, approaches, processes, or variations thereof, usingany devices, equipment, apparatuses, systems, or variations thereof,using any of the build material, printing mixture, ink, yield-stresssupport material, or other material compositions described herein orvariations thereof, are all contemplated and covered by the presentdisclosure. None of the examples provided are intended to, nor shouldthey, limit in any way the scope of the present disclosure.

Every document cited or referenced herein, including any crossreferenced or related patent or application is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document and/or the mention ofmethods or apparatuses as being conventional, typical, usual, or thelike is not, and should not be taken as an acknowledgement or any formof suggestion that the reference or mentioned method/apparatus is priorart with respect to any invention disclosed or claimed herein or that italone, or in any combination with any other reference or references,teaches, suggests or discloses any such invention or forms part of thecommon general knowledge in any country in the world. Further, to theextent that any meaning or definition of a term in this documentconflicts with any meaning or definition of the same term in a documentincorporated by reference, the meaning or definition assigned to thatterm in this document shall govern.

The various portions of the present disclosure, such as the Background,Summary, Brief Description of the Drawings, and Abstract sections, areprovided to comply with requirements of the MPEP and are not to beconsidered an admission of prior art or a suggestion that any portion orpart of the disclosure constitutes common general knowledge in anycountry in the world. The present disclosure is provided as a discussionof the inventor's own work and improvements based on the inventor's ownwork. See, e.g., Riverwood Intl Corp. v. R.A. Jones & Co., 324 F.3d1346, 1354 (Fed. Cir. 2003).

1. An apparatus for additive manufacturing, the apparatus comprising: areservoir configured to contain a supply of a printing mixture; a nozzlefluidically coupled to the reservoir, the nozzle being dimensioned andconfigured to reduce or eliminate nozzle movement-induced liquefactionof a yield-stress support bath during disposing of said printing mixtureinto said yield-stress support bath; and a computing device in operablecommunication with the nozzle, the computing device being configured tocause communication of the printing mixture from the reservoir to thenozzle and into the yield-stress support bath, the computing devicebeing further configured to cause movement of the nozzle into, through,and out of the yield-stress support bath.
 2. The apparatus of claim 1,wherein the computing device is configured to guide movement of thenozzle during dispensing of the printing mixture into the yield-stresssupport bath such that an intermediate article is formed from theprinting mixture, the intermediate article being suspended within theyield-stress support bath.
 3. The apparatus of claim 2, wherein theapparatus is configured to allow the printing mixture to partiallycoagulate in the yield-stress support bath to form the intermediatearticle.
 4. The apparatus of claim 2, wherein the apparatus isconfigured to expose the intermediate article to a post-treatmentcoagulation solution to cause the intermediate article to furthercoagulate, forming a finished article.
 5. The apparatus of claim 1,wherein the printing mixture comprises acrylonitrile butadiene styreneat least partially dissolved in dimethyl sulfoxide.
 6. The apparatus ofclaim 1, wherein the nozzle comprises a dispensing tip having an outsidediameter between about 0.05 inches and about 0.5 inches.
 7. An apparatusfor additive manufacturing, the apparatus comprising: a reservoirconfigured to contain a supply of a printing mixture; a nozzlefluidically coupled to the reservoir, the nozzle being dimensioned andconfigured to reduce or eliminate nozzle movement-induced liquefactionof a yield-stress support bath during movement of the nozzle through theyield-stress support bath; and a computing device in operablecommunication with the nozzle, the computing device being configured tocause the apparatus to perform at least: communicating a volume of theprinting mixture from the reservoir, through the nozzle, and into aportion of the yield-stress support bath, moving the nozzle along apathway through the yield-stress support bath, communicating one or moreadditional volumes of the printing mixture from the reservoir, throughthe nozzle, and into one or more additional portions of the yield-stresssupport bath along the pathway through the yield-stress support bath,and allowing the volume of the printing mixture and the one or moreadditional volumes of the printing mixture to partially coagulate in theyield-stress support bath.
 8. The apparatus of claim 7, wherein theallowing the volume of the printing mixture and the one or moreadditional volumes of the printing mixture to partially coagulate in theyield-stress support bath forms an intermediate article suspended withinthe yield-stress support bath.
 9. The apparatus of claim 8, wherein theapparatus is configured to allow the volume of the printing mixture andthe one or more additional volumes of the printing mixture to onlypartially coagulate in the yield-stress support bath to form theintermediate article.
 10. The apparatus of claim 8, wherein theapparatus is configured to expose the intermediate article to apost-treatment coagulation solution to cause the intermediate article tofurther coagulate, forming a finished article.
 11. The apparatus ofclaim 7, wherein the printing mixture comprises acrylonitrile butadienestyrene at least partially dissolved in dimethyl sulfoxide.
 12. Theapparatus of claim 7, wherein the nozzle comprises a dispensing tiphaving an outside diameter between about 0.05 inches and about 0.5inches.
 13. An apparatus for additive manufacturing, the apparatuscomprising: a reservoir configured to contain a supply of a printingmixture; a yield-stress support bath containing a yield-stress supportbath material; a nozzle fluidically coupled to the reservoir, the nozzlebeing dimensioned and configured to be disposed within the yield-stresssupport bath material for printing of the printing mixture into theyield-stress support bath; and a computing device in operablecommunication with the nozzle, the computing device being configured tocause the apparatus to perform at least: determining a nozzle pathwaythrough the yield-stress support bath and corresponding volumes of theprinting mixture to print at a plurality of points along the pathway toachieve an intermediate article that corresponds to a finished article,moving the nozzle along the pathway through the yield-stress supportbath, wherein the nozzle is dimensioned and configured to reduce oreliminate nozzle movement-induced liquefaction of the yield-stresssupport bath material during movement of the nozzle through theyield-stress support bath, communicating the corresponding volumes ofthe printing mixture from the reservoir, through the nozzle, and intothe yield-stress support bath material at the plurality of points alongthe pathway through the yield-stress support bath, and allowing thecorresponding volumes of the printing mixture to partially coagulate inthe yield-stress support bath material to form the intermediate articlethat corresponds to the finished article.
 14. The apparatus of claim 13,wherein the apparatus is configured to allow the corresponding volumesof the printing mixture disposed along the pathway through theyield-stress support bath to only partially coagulate in theyield-stress support bath material to form the intermediate article. 15.The apparatus of claim 13, wherein the apparatus is configured to carryout the additive manufacturing at about room temperature.
 16. Theapparatus of claim 13, wherein the printing mixture comprisesacrylonitrile butadiene styrene at least partially dissolved in dimethylsulfoxide.
 17. The apparatus of claim 13, wherein the nozzle comprises adispensing tip having an outside diameter between about 0.05 inches andabout 0.5 inches.
 18. The apparatus of claim 13, wherein the computingdevice is further configured to cause the apparatus to perform: mixingone or more cross-linking materials with one or more solvents to formthe printing mixture.
 19. The apparatus of claim 13, wherein thecomputing device is further configured to cause the apparatus toperform: disposing a rheological additive material into one or moresecond solvents or a solvent/non-solvent mixture to form a support bathmaterial mixture; and allowing the support bath material mixture tobecome at least partially solid-like, forming the yield-stress supportbath material.
 20. The apparatus of claim 13, wherein the computingdevice is further configured to cause the apparatus to perform: exposingthe intermediate article to a post-treatment coagulation solution tofurther solidify the intermediate article, forming the finished article.